What is a TRANSISTOR
- Transistor is a semiconductor device which is used in electronic circuits to amplify or switch signals.
- It is mainly used to CONTROL THE CUREENT FLOW.
App:
- Amplification: Increasing the strength of an electrical signal.
- Switching: Controlling the flow of current on and off.
Vdo transistor working: https://youtu.be/7ukDKVHnac4?si=0AgJhrte8LMvCEun
- Diode: A diode is formed when a silicon is doped with N type (Phosphrous) and P type (Boron)
- Phosphorous has 5 valence electron (N) and boron has 3 valence electron (P), electrons from N travel to P forming depletion region.
- In FORWARD BIAS more electrons get diffused in N type, and as there are holes in p type... electrons are drifted towards P type, casuing current to flow.
- Emitter (heavily doped), base, Collector.
- one side is forward biased, another is reverse biased.
- small amount of base current is amplified at collector current.
- To make transistor work as amplifier CONTROL THE CURRENT IN TRANSISTOR
- To make transistor work as switch CONTROL THE THRESHOLD VOLATGE
Modes of Operation
-
Active region: Current flows from E to C - Vc>Vb>Ve
- emitter-base is FB
- collector base is RB
-
Cutoff region: No current flows - Ve>Vb
- emitter-base is RB
- collector base is RB
-
saturation region: Vb>Ve & Vb>Vc
- emitter-base is FB
- collector base is FB
semiconductor devices that control the flow of current between a source and a drain terminal using an Voltage.
Junction Field-Effect Transistors (JFETs):
- The gate terminal is a PN junction.
- The gate voltage controls the width of the channel between the source and drain.
Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs):
- The gate terminal is insulated from the channel by a layer of oxide.
- The gate voltage controls the formation of a channel between the source and drain.
MOSFET
Vdo:https://youtu.be/stM8dgcY1CA?si=d5HHqySzxiSV1mjt
Capacitor: It consists of an insulator sandwiched between two metal plates.
- Electric field is induced between two metal plates.
- one metal plate is removed and another metal plate with insulator is placed on MOSFET as GATE terminal.
Working;
- when voltage is applied between GATE and SUBSTRATE, electrons from CAPACITOR are fed into P type substrate
- Number of electrons increases in p-type substrate
- Electric field from CAP is induced in substrate causing large number of electrons attract to the GATE terminal
- Electrons combine with the holes and break the deplition region
- This introduces channel between two N-wells
- On providing voltage between drain and source, current flows from Source to drain (MOSFET TURNS ON)
Depletion Type of MOSFET
- Channel is already present
- MOSFET IS works even at Vgs=0
- At Vgs>0, Drain current (Id) increases
- At Vgs<0, Drain current (Id) decreases
- On applying Vds (drain to source), current starts to flow from source to drain.
- After pinch off voltage (Too much of Vds) the current gets saturated.
Drain and transfer Characteristics
Transfer characteristics are Input vs Output
- Depletion mode is device OFF
- Enhancement mode is device ON
Enhancement Type of MOSFET
- Channel is formed
- When Vgs>0, minority carriers (electrons) from p substrate are attracted towards gate.
- As Vgs increases, drain current also increases.
- INVERSION: the p-type near gate is inverted to n-type, forming a channel
- When Vds is applied the current starts to flow from source to drain
- Vgd (voltage between gate and drain ) = Vgs - Vds
- IF Vds = 0V : Vgd=Vgs (Uniform depletion width)
- If Vds > 0v : Vgd decreases (More e- are pulled by drain, hence channel width decreases) Non-Uniform
- If Vds = Vgs - Vt : Vgd = Vt ( Channel will become very narrow near DRAIN, making the MOSFET OFF) : Pinch OFF voltage occurs
OP AMP
App : ADC, DAC, Oscillators,
- Slewrate: how fast the Op-Amp reaches its final value
- Common mode rejection ratio : The ability of Op-Amp to reject the input when same voltage is applied at both the terminals.(For better accuracy)
- Open Loop gain is generally between 10^5 - 10^6
- A differential op-amp is a type of operational amplifier (op-amp) that amplifies the difference between two input signals.
- The amplified signal is always in between V+ and V-